1996 Subaru Legacy security light flashes and doesn't run

The head gaskets were replaced, but it ran fine before that, just overheated. The heads were resurfaced. The mechanic started it and ran it without oil for about a minute. That's when the security light came on. Now it will run for about 10 seconds and then stall. If we wait for a few hours it will start again and then shut off after 10 seconds. To try to shut off the security light we unlocked it with a key and put the key in the ignition immediately. The other thing we did was look for a code alarm programming button behind kick panel to the left of the steering wheel under the dash and we couldn't find it. It seems to run fine for the 10 seconds, no knocking or other unusual sounds. Any thoughts?